Selective para-xylene production by toluene methylation

ABSTRACT

There is provided a process for the selective production of para-xylene which comprises reacting toluene with methanol in the presence of a catalyst comprising a porous crystalline material having a Diffusion Parameter for 2,2 dimethylbutane of about 0.1-15 sec −1  when measured at a temperature of 120° C. and a 2,2 dimethylbutane pressure of 60 torr (8 kPa). The porous crystalline material is preferably a medium-pore zeolite, particularly ZSM-5, which has been severely steamed at a temperature of at least 950° C. The porous crystalline material is preferably combined with at least one oxide modifier, preferably including phosphorus, to control reduction of the micropore volume of the material during the steaming step.

There is provided a process for the selective production of para-xyleneby catalytic methylation of toluene in the presence of a solid catalyst.There is also provided a method for preparing a catalyst which isparticularly suited for this reaction.

Of the xylene isomers, para-xylene is of particular value since it isuseful in the manufacture of terephthalic acid which is an intermediatein the manufacture of synthetic fibers. Equilibrium mixtures of xyleneisomers either alone or in further admixture with ethylbenzene generallycontain only about 24 wt. % para-xylene and separation of p-xylene fromsuch mixtures has typically required superfractionation and multistagerefrigeration steps. Such processes have involved high operation costsand resulted in only limited yields. There is therefore a continuingneed to provide processes which are highly selective for the productionof p-xylene.

One known method for producing xylenes involves the alkylation oftoluene with methanol over a solid acid catalyst. Thus the alkylation oftoluene with methanol over cation-exchanged zeolite Y has been describedby Yashima et al. in the Journal of Catalysis 16, 273-280 (1970). Theseworkers reported selective production of para-xylene over theapproximate temperature range of 200 to 275° C., with the maximum yieldof para-xylene in the mixture of xylenes, i.e. about 50% of the xyleneproduct mixture, being observed at 225° C. Higher temperatures werereported to result in an increase in the yield of meta-xylene and adecrease in production of para and ortho-xylenes.

U.S. Pat. No. 3,965,209 to Butter et al. and U.S. Pat. No. 4,067,920 toKaeding teach processes for producing para-xylene in low conversion andhigh selectivity by reaction of toluene with methanol over a zeolitehaving a Constraint Index of 1-12, such as ZSM-5. In Butter et al thezeolite is steamed at a temperature of 250-1000° C. for 0.5-100 hours toreduce the acid activity of the zeolite, as measured by its alphaactivity, to less than 500 and preferably from in excess of zero to lessthan 20.

U.S. Pat. No. 4.001,346 to Chu relates to a process for the selectiveproduction of para-xylene by methylation of toluene in the presence of acatalyst comprising a crystalline aluminosilicate zeolite which hasundergone prior treatment to deposit a coating of between about 15 andabout 75 wt. % of coke thereon.

U.S. Patent No. 4,097,543 to Haag et al. relates to a process for theselective production of para-xylene (up to about 77%) bydisproportionation of toluene in the presence of a crystallinealuminosilicate catalyst which has undergone precoking to deposit acoating of at least about 2 wt. % coke thereon.

U.S. Pat. No. 4,380,685 to Chu relates to a process for para-selectivearomatics alkylation, including the methylation of toluene, over azeolite, such as ZSM-5, which has a constraint index of 1-12 and whichhas been combined with phosphorus and a metal selected from iron andcobalt. Chu indicates that the catalyst can optionally be modified(without specifying the effect of the modification) by steaming at atemperature of 250-1000° C., preferably 400-700° C. for 0.5-100 hours,preferably 1-24 hours.

U.S. Pat. No. 4,554,394 to Forbus and Kaeding teach the use ofphosphorus-treated zeolite catalysts for enhancing para-selectivity inaromatics conversion processes. U.S. Pat. No. 4,623,633 to Young relatesto the use of thermal shock calcination of aluminosilicates to produceup to 66% para-xylene selectivity.

The use of phosphorus modified ZSM-5 fluid bed catalysts as additivecatalysts to improve the olefin yield in fluid catalytic cracking (FCC)is described in U.S. Pat. No. 5,389,232 to Adewuyi et al. and in U.S.Pat. No. 5,472,594 to Tsang et al.

According to the invention, it has now been found that certain porouscrystalline materials having specific and closely defined diffusioncharacteristics, such as can be obtained by unusually severe steaming ofZSM-5 containing an oxide modifier, exhibit improved selectivity for thealkylation of toluene with methanol such that the xylene productcontains at least about 90% of the paraisomer isomer at per-pass tolueneconversions of at least about 15%.

In one aspect, the invention resides in a process for the selectiveproduction of para-xylene which comprises reacting toluene with methanolunder alkylation conditions in the presence of a catalyst comprising aporous crystalline material having a Diffusion Parameter for2,2-dimethylbutane of about 0.1-15 sec-⁻¹ when measured at a temperatureof 120° C. and a 2,2-dimethylbutane pressure of 60 torr (8 kPa).

Preferably, the porous crystalline material has a Diffusion Parameter ofabout 0.5-10 sec⁻¹.

Preferably, the catalyst contains at least one oxide modifier and morepreferably at least one oxide modifier selected from oxides of elementsof Groups IIA, IIIA, IIIB, IVA, VA, VB and VIA of the Periodic Table.Most preferably the oxide modifier is selected from oxides of boron,magnesium, calcium, lanthanum and most preferably phosphorus.

Preferably, the catalyst contains about 0.05 to about 20, morepreferably about 0.1 to about 10 and most preferably about 0.1 to about5, wt % of the oxide modifier based on elemental modifier.

Preferably, the catalyst has an alpha value less than 50 and preferablyless than 10.

In a further aspect, the invention resides in a method for producing acatalyst for use in the selective production of para-xylene by reactingtoluene with methanol, said method comprising the steps of:

(a) starting with a porous crystalline material having a DiffusionParameter for 2,2-dimethylbutane in excess of 15 sec⁻¹ when measured ata temperature of 120° C. and a 2,2-dimethylbutane pressure of 60 torr (8kPa); and

(b) contacting the material of step (a) with steam at a temperature ofat least about 950° C. to reduce the Diffusion Parameter thereof for2,2-dimethylbutane to about 0.1-15 sec⁻¹ when measured at a temperatureof 120° C. and a 2,2-dimethylbutane pressure of 60 torr (8 kPa), themicropore volume of the steamed material being at least 50% of theunsteamed material.

Preferably, said porous crystalline material used in step (a) comprisesan aluminosilicate zeolite having a silica to alumina molar ratio of atleast 250.

The present invention provides a process for alkylating toluene withmethanol to selectively produce p-xylene in high yield and with a highper-pass conversion of toluene. The process employs a catalyst whichcomprises a porous crystalline material having a Diffusion Parameter for2,2-dimethylbutane of about 0.1-15 sec⁻¹, and preferably 0.5-10 sec⁻¹,when measured at a temperature of 120° C. and a 2,2-dimethylbutanepressure of 60 torr (8 kPa).

As used herein, the Diffusion Parameter of a particular porouscrystalline material is defined as D/r²×10⁶, wherein D is the diffusioncoefficient (cm²/sec) and r is the crystal radius (cm). The requireddiffusion parameters can be derived from sorption measurements providedthe assumption is made that the plane sheet model describes thediffusion process. Thus for a given sorbate loading Q, the value Q/Q∞,where Q∞ is the equilibrium sorbate loading, is mathematically relatedto (Dt/r²)^(½) where t is the time (sec) required to reach the sorbateloading Q. Graphical solutions for the plane sheet model are given by J.Crank in “The Mathematics of Diffusion”, Oxford University Press, ElyHouse, London, 1967.

The porous crystalline material employed in the process of the inventionis preferably a medium-pore size aluminosilicate zeolite. Medium porezeolites are generally defined as those having a pore size of about 5 toabout 7 Angstroms, such that the zeolite freely sorbs molecules such asn-hexane, 3-methylpentane, benzene and p-xylene. Another commondefinition for medium pore zeolites involves the Constraint Index testwhich is described in U.S. Pat. No. 4,016,218, which is incorporatedherein by reference. In this case, medium pore zeolites have aConstraint Index of about 1-12, as measured on the zeolite alone withoutthe introduction of oxide modifiers and prior to any steaming to adjustthe diffusivity of the catalyst. In addition to the medium-pore sizealuminosilicate zeolites, other medium pore acidic metallosilicates,such as silicoaluminophosphates (SAPOs), can be used in the process ofthe invention.

Particular examples of suitable medium pore zeolites include ZSM-5,ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM48, and MCM-22, with ZSM-5and ZSM-11 being particularly preferred.

Zeolite ZSM-5 and the conventional preparation thereof are described inU.S. Pat. No. 3,702,886, the disclosure of which is incorporated hereinby reference. Zeolite ZSM-11 and the conventional preparation thereofare described in U.S. Pat. No. 3,709,979, the disclosure of which isincorporated herein by reference. Zeolite ZSM-12 and the conventionalpreparation thereof are described in U.S. Pat. No. 3,832,449, thedisclosure of which is incorporated herein by reference. Zeolite ZSM-23and the conventional preparation thereof are described in U.S. Pat. No.4,076,842, the disclosure of which is incorporated herein by reference.Zeolite ZSM-35 and the conventional preparation thereof are described inU.S. Pat. No. 4,016,245, the disclosure of which is incorporated hereinby reference. ZSM-48 and the conventional preparation thereof is taughtby U.S. Pat. No. 4,375,573, the disclosure of which is incorporatedherein by reference. MCM-22 is disclosed in U.S. Pat. No. 5,304,698 toHusain; U.S. Pat. No. 5,250,277 to Kresge et al.; U.S. Pat. No.5,095,167 to Christensen; and U.S. Pat. No. 5,043,503 to Del Rossi etal., the disclosure of which patents are incorporated by reference.

Preferably, the zeolite employed in the process of the invention isZSM-5 having a silica to alumina molar ratio of at least 250, asmeasured prior to any treatment of the zeolite to adjust itsdiffusivity.

The medium pore zeolites described above are preferred for the processof the invention since the size and shape of their pores favor theproduction of p-xylene over the other xylene isomers. However,conventional forms of these zeolites have Diffusion Parameter values inexcess of the 0.1-15 sec⁻¹ range required for the process of theinvention. The required diffusivity for the present catalyst can beachieved by severely steaming the catalyst so as to effect a controlledreduction in the micropore volume of the catalyst to not less than 50%,and preferably 50-90%, of that of the unsteamed catalyst. Reduction inmicropore volume is derived by measuring the n-hexane adsorptioncapacity of the catalyst, before and after steaming, at 90° C. and 75torr n-hexane pressure.

Steaming of the porous crystalline material is effected at a temperatureof at least about 950° C., preferably about 950 to about 1075° C., andmost preferably about 1000 to about 1050° C. for about 10 minutes toabout 10 hours, preferably from 30 minutes to 5 hours.

To effect the desired controlled reduction in diffusivity and microporevolume, it may be desirable to combine the porous crystalline material,prior to steaming, with at least one oxide modifier, preferably selectedfrom oxides of the elements of Groups IIA, IIIA, IIIB, IVA, VA, VB andVIA of the Periodic Table (IUPAC version). Most preferably, said atleast one oxide modifier is selected from oxides of boron, magnesium,calcium, lanthanum and most preferably phosphorus. In some cases, it maybe desirable to combine the porous crystalline material with more thanone oxide modifier, for example a combination of phosphorus with calciumand/or magnesium, since in this way it may be possible to reduce thesteaming severity needed to achieve a target diffusivity value. Thetotal amount of oxide modifier present in the catalyst, as measured onan elemental basis, may be between about 0.05 and about 20 wt. %, andpreferably is between about 0.1 and about 10 wt. %, based on the weightof the final catalyst.

Where the modifier includes phosphorus, incorporation of modifier in thecatalyst of the invention is conveniently achieved by the methodsdescribed in U.S. Pat. Nos. 4,356.338, 5,110,776, 5,231,064 and5,348,643, the entire disclosures of which are incorporated herein byreference. Treatment with phosphorus-containing compounds can readily beaccomplished by contacting the porous crystalline material, either aloneor in combination with a binder or matrix material, with a solution ofan appropriate phosphorus compound, followed by drying and calcining toconvert the phosphorus to its oxide form. Contact with thephosphorus-containing compound is generally conducted at a temperatureof about 25° C. and about 125° C. for a time between about 15 minutesand about 20 hours. The concentration of the phosphorus in the contactmixture may be between about 0.01 and about 30 wt. %.

After contacting with the phosphorus-containing compound, the porouscrystalline material may be dried and calcined to convert the phosphorusto an oxide form. Calcination can be carried out in an inert atmosphereor in the presence of oxygen, for example, in air at a temperature ofabout 150 to 750° C., preferably about 300 to 500° C., for at least 1hour, preferably 3-5 hours.

Similar techniques known in the art can be used to incorporate othermodifying oxides into the catalyst of the invention.

Representative phosphorus-containing compounds which may be used toincorporate a phosphorus oxide modifier into the catalyst of theinvention include derivatives of groups represented by PX₃, RPX₂, R₂PX,R₃P, X₃PO, (XO)₃PO, (XO)₃P, R₃P═O, R₃P═S, RPO₂, RPS₂, RP(O)(OX)₂,RP(S)(SX)₂, R₂P(O)OX, R₂P(S)SX, RP(OX)₂, RP(SX)₂, ROP(OX)₂, RSP(SX)₂,(RS)₂PSP(SR)₂, and (RO)₂POP(OR)₂, where R is an alkyl or aryl, such asphenyl radical, and X is hydrogen, R, or halide. These compounds includeprimary, RPH₂, secondary, R₂PH, and tertiary, R₃P, phosphines such asbutyl phosphine, the tertiary phosphine oxides, R₃PO, such as tributylphosphine oxide, the tertiary phosphine sulfides, R₃PS, the primary,RP(O)(OX)₂, and secondary, R₂P(O)OX, phosphonic acids such as benzenephosphonic acid, the corresponding sulfur derivatives such as RP(S)(SX)₂and R₂P(S)SX, the esters of the phosphonic acids such as dialkylphosphonate, (RO)₂P(O)H, dialkyl alkyl phosphonates, (RO)₂P(O)R, andalkyl dialkylphosphinates, (RO)P(O)R₂; phosphinous acids, R₂POX, such asdiethylphosphinous acid, primary, (RO)P(OX)₂, secondary, (RO)₂POX, andtertiary, (RO)₃P, phosphites, and esters thereof such as the monopropylester, alkyl dialkylphosphinites, (RO)PR₂, and dialkyl alkyphosphinite,(RO)₂PR, esters. Corresponding sulfur derivatives may also be employedincluding (RS)₂P(S)H, (RS)₂P(S)R, (RS)P(S)R₂, R₂PSX, (RS)P(SX)₂,(RS)₂PSX, (RS)₃P, (RS)PR₂, and (RS)₂PR. Examples of phosphite estersinclude trimethylphosphite, triethylphosphite, diisopropylphosphite,butylphosphite, and pyrophosphites such as tetraethylpyrophosphite. Thealkyl groups in the mentioned compounds preferably contain one to fourcarbon atoms.

Other suitable phosphorus-containing compounds include ammonium hydrogenphosphate, the phosphorus halides such as phosphorus trichloride,bromide, and iodide, alkyl phosphorodichloridites, (RO)PCl₂,dialkylphosphorochloridites, (RO)₂PCl, dialkylphosphinochloroidites,R₂PCl, alkyl alkylphosphonochloridates. (RO)(R)P(O)Cl, dialkylphosphinochloridates, R₂P(O)Cl, and RP(O)Cl₂. Applicable correspondingsulfur derivatives include (RS)PCl₂, (RS)₂PCl. (RS)(R)P(S)Cl, andR₂P(S)Cl.

Particular phosphorus-containing compounds include ammonium phosphate,ammonium dihydrogen phosphate, diammonium hydrogen phosphate, diphenylphosphine chloride, trimethylphosphite. phosphorus trichloride,phosphoric acid, phenyl phosphine oxychloride, trimethylphosphate,diphenyl phosphinous acid, diphenyl phosphinic acid,diethyichlorothiophosphate, methyl acid phosphate, and otheralcohol-P₂O₅ reaction products.

Representative boron-containing compounds which may be used toincorporate a boron oxide modifier into the catalyst of the inventioninclude boric acid, trimethylborate, boron oxide, boron sulfide, boronhydride, butylboron dimethoxide, butylboric acid, dimethylboricanhydride, hexamethylborazine, phenyl boric acid, triethylborane,diborane and triphenyl boron.

Representative magnesium-containing compounds include magnesium acetate,magnesium nitrate, magnesium benzoate, magnesium propionate, magnesium2-ethylhexoate, magnesium carbonate, magnesium formate, magnesiumoxylae, magnesium bromide, magnesium hydride, magnesium lactate,magnesium laurate, magnesium oleate, magnesium palmitate, magnesiumsalicylate, magnesium stearate and magnesium sulfide.

Representative calcium-containing compounds include calcium acetate,calcium acetylacetonate, calcium carbonate, calcium chloride, calciummethoxide, calcium naphthenate, calcium nitrate, calcium phosphate,calcium stearate and calcium sulfate.

Representative lanthanum-containing compounds include lanthanum acetate,lanthanum acetylacetonate, lanthanum carbonate, lanthanum chloride,lanthanum hydroxide, lanthanum nitrate, lanthanum phosphate andlanthanum sulfate.

The porous crystalline material employed in the process of the inventionmay be combined with a variety of binder or matrix materials resistantto the temperatures and other conditions employed in the process. Suchmaterials include active and inactive materials such as clays, silicaand/or metal oxides such as alumina. The latter may be either naturallyoccurring or in the form of gelatinous precipitates or gels includingmixtures of silica and metal oxides. Use of a material which is active,tends to change the conversion and/or selectivity of the catalyst andhence is generally not preferred. Inactive materials suitably serve asdiluents to control the amount of conversion in a given process so thatproducts can be obtained economically and orderly without employingother means for controlling the rate of reaction. These materials may beincorporated into naturally occurring clays, e.g., bentonite and kaolin,to improve the crush strength of the catalyst under commercial operatingconditions. Said materials, i.e., clays, oxides, etc., function asbinders for the catalyst. It is desirable to provide a catalyst havinggood crush strength because in commercial use it is desirable to preventthe catalyst from breaking down into powder-like materials. These clayand/or oxide binders have been employed normally only for the purpose ofimproving the crush strength of the catalyst.

Naturally occurring clays which can be composited with the porouscrystalline material include the montmoillonite and kaolin family, whichfamilies include the subbentonites, and the kaolins commonly known asDixie, McNamee, Georgia and Florida clays or others in which the mainmineral constituent is halloysite, kaolinite, dickite, nacrite, oranauxite. Such clays can be used in the raw state as originally mined orinitially subjected to calcination, acid treatment or chemicalmodification.

In addition to the foregoing materials, the porous crystalline materialcan be composied with a porous matrix material such as silica-alumina,silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia,silica-titania as well as ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia silica-alumina-magnesiaand silica-magnesia-zirconia.

The relative proportions of porous crystalline material and inorganicoxide matrix vary widely, with the content of the former ranging fromabout 1 to about 90% by weight and more usually, particularly when thecomposite is prepared in the form of beads, in the range of about 2 toabout 80 wt. % of the composite.

Preferably, the binder material comprises silica or a kaolin clay.

Procedures for preparing silica-bound zeolites, such as ZSM-5, aredescribed in U.S. Pat. Nos. 4,582,815; 5,053,374; and 5,182,242. Aparticular procedure for binding ZSM-5 with a silica binder involves anextrusion process.

The porous crystalline material may be combined with a binder in theform of a fluidized bed catalyst. This fluidized bed catalyst maycomprise clay in the binder thereof, and may be formed by a spray-dryingprocess to form catalyst particles having a particle size of 20-200microns.

The catalyst of the invention may optionally be precoked. The precokingstep is preferably carried out by initially utilizing the uncokedcatalyst in the toluene methylation reaction, during which coke isdeposited on the catalyst surface and thereafter controlled within adesired range, typically from about 1 to about 20 wt. % and preferablyfrom about 1 to about 5 wt. %, by penodic regeneration by exposure to anoxygen-containing atmosphere at an elevated temperature.

One of the advantages of the catalyst described herein is its ease ofregenerability. Thus, after the catalyst accumulates coke as itcatalyzes the toluene methylation reaction, it can easily be regeneratedby burning off a controlled amount of coke in a partial combustionatmosphere in a regenerator at temperatures in the range of from about400 to about 700° C. The coke loading on the catalyst may thereby bereduced or substantially eliminated in the regenerator. If it is desiredto maintain a given degree of coke loading, the regeneration step may becontrolled such that the regenerated catalyst returning to the toluenemethylation reaction zone is coke-loaded at the desired level.

The present process may suitably be carried out in fixed, moving, orfluid catalyst beds. If it is desired to continuously control the extentof coke loading, moving or fluid bed configurations are preferred. Withmoving or fluid bed configurations, the extent of coke loading can becontrolled by varying the severity and/or the frequency of continuousoxidative regeneration in the catalyst regenerator.

The process of the present invention is generally conducted at atemperature between about 500 and about 700° C., preferably betweenabout 500 and about 600° C., a pressure of between about 1 atmosphereand 1000 psig (100 and 7000 kPa), a weight hourly space velocity ofbetween about 0.5 and 1000, and a molar ratio of toluene to methanol (inthe reactor charge) of at least about 0.2, e.g., from about 0.2 to about20. The process is preferably conducted in the presence of addedhydrogen and/or added water such that the molar ratio of hydrogen and/orwater to toluene +methanol in the feed is between about 0.01 and about10.

Using the process of the invention, toluene can be alkylated withmethanol so as to produce para-xylene at a selectivity of at least about90 wt % (based on total C₈ aromatic product) at a per-pass tolueneconversion of at least about 15 wt % and a trimethylbenzene productionlevel less than 1 wt %,

The invention will now be more particularly described in the followingExamples and the accompanying drawing, in which:

FIG. 1 is a graph of Diffusion Parameter against para-xylene yield andpara-xylene selectivity for the catalyst of Examples 10-14; and

FIGS. 2 and 3 are graphs of steaming temperature against n-hexanesorption capacity and Diffusion Parameter respectively for the catalystsof Example 15.

In the Examples, micropore volume (n-hexane) measurements were made on acomputer controlled (Vista/Fortran) duPont 951 Thermalgravimetricanalyzer. Isotherms were measured at 90° C. and adsorption values takenat 75 torr n-hexane. The diffusion measurements were made on a TAInstruments 2950 Thermalgravimetric Analyzer equipped with a ThermalAnalysis 2000 controller, a gas switching accessory and an automaticsample changer. Diffusion measurements were made at 120° C. and 60 torr2.2-dimethylbutane. Data were plotted as uptake versus square root oftime. Fixed bed catalytic testing was conducted using a ⅜″ (1 cm)outside diameter, down-flow reactor using a two gram catalyst sample.The product distribution was analyzed with an on-line Varian 3700 GC(Supelcowax 10 capillary column, 30 m in length, 0.32 mm internaldiameter, and 0.5 μm film thickness).

EXAMPLES 1-5

Five samples of a composite catalyst containing 2.9 wt. % phosphorus and10 wt % of a 450:1 SiO₂/Al₂O₃ ZSM-5 in a binder comprisingsilica-alumina and clay were steamed for 0.75 hours, one atmospheresteam at 975° C. (Example 1), 1000° C. (Example 2), 1025° C. (Example3), 1050° C. (Example 4) and 1075° C. (Example 5). The effect ofsteaming temperature on the n-hexane sorption capacity (Q) compared tothat of the unsteamed catalyst (10.7 mg/g) and on the DiffusionParameter (D/r²×10⁶) is summarized in Table 1 below.

Samples of the five steamed catalysts were then used in toluenemethylation tests on a feed comprising toluene, methanol and water suchthat toluene/MeOH molar ratio=2 and H₂O/HC molar ratio=2 (whereHC=toluene+methanol). The tests were conducted at 600° C., 40 psig (380kPa) and HC WHSV=4 in the presence of hydrogen such that H₂/HC molarratio=2 The results of Examples 2-5 are summarised in Table 2.

TABLE 1 % retention of Catalyst Steaming initial sorption D/r2 ID Temp(° C.) Q (n-C₆, mg/g) capacity sec⁻¹ (×10⁶) Ex. 1 975 10.3 96 21.2 Ex. 21000 9.7 91 16.4 Ex. 3 1025 9.1 85 10.2 Ex. 4 1050 8.4 79 3.2 Ex. 5 10756.5 61 0.3

TABLE 2 Example Example Example Example 2 3 4 5 Temp, ° C. 600.0 600.0600.0 600.0 Pressure, psig 40.5 42.8 40.3 43.2 WHSV 4.0 4.0 4.0 4.0 Timeon Stream, hr 4.8 20.6 5.1 5.0 Product Distribution (wt %) C5− 1.42 0.730.99 1.44 MeOH 0.02 0.17 0.21 1.85 BENZENE 0.25 0.13 0.20 0.27 TOLUENE61.82 62.41 66.27 81.63 EB 0.06 0.06 0.06 0.04 P-XYL 30.38 32.21 30.5214.26 M-XYL 3.17 2.00 0.68 0.13 O-XYL 1.37 0.94 0.33 0.11 ETOL 0.30 0.330.31 0.14 TMBENZENE 1.05 0.92 0.37 0.08 C10+ 0.15 0.10 0.04 0.04 100.00100.00 100.00 100.00 Performance Data Toluene Conv. % 33.21 32.56 28.3911.80 MeOH Conv. % 99.71 97.76 97.76 75.12 MeOH Utilization, 62.08 63.7257.53 34.26 mol % p-Xylene Selectivity, % 86.99 91.64 96.80 98.35 XyleneYield on 37.73 37.98 34.07 15.67 Toluene, wt % p-Xylene Yield on Tol,32.8 34.8 33.0 15.4 wt % Xylenes/Aromatic 95.1 95.8 97.0 96.2 Product,wt %

From Table 2 it will be seen, with the catalyst of Examples 1-5,steaming at a temperature in excess of 1000° C. was necessary to reducethe D/r2 value below 15 and with the Example 2 catalyst (steamed at1000° C. to a D/r2 value of 16.4), the p-selectivity of the catalyst wasbelow 87%. As the steaming temperature increased above 1000 C. to 1075°C, the para-xylene selectivity increased but with the catalyst steamedat 1075° C. this was accompanied by a significant decrease in theparaxylene yield and the methanol utilization (moles of xyleneproduced/moles of methanol converted).

EXAMPLES 6-9

A second composite catalyst containing 4.5 wt % phosphorus and 10 wt. %of a 450:1 SiO₂/Al₂O₃ ZSM-5 in a binder comprising silica-alumina andclay was divided into four samples which were steamed for 0.75 hours,one atmosphere steam at 950° C. (Example 6), 975° C. (Example 7), 1000°C. (Example 8), and 1025° C. (Example 9). The effect of steamingtemperature on the n-hexane sorption capacity (Q) and DiffusionParameter (D/r²×10⁶) of these catalysts is summarized in Table 3 below.

Samples of the four steamed catalysts were then used in toluenemethylation tests conducted as in Examples 2-5 with the HC WHSV=4. Theresults of Examples 6-9 are summarised in Table 4.

TABLE 3 % retention Steaming Q (n-C₆, of initial D/r2 Catalyst ID Temp(° C.) mg/g) sorption capacity sec⁻¹ (×10⁶) Unsteamed 12.7 21.7 SampleEx. 6 950 9.4 74 6.3 Ex. 7 975 7.2 57 5.3 Ex. 8 1000 7.9 62 1.92 Ex. 91025 7.0 55 0.84

TABLE 4 Example Example Example Example 6 7 8 9 Temp, ° C. 600.0 600.0600 600 Pressure, psig 44.3 43.1 45.3 42.0 WHSV 4.0 4.0 4.0 4.0 Time onStream, hr 6.3 5.9 5.9 5.9 Product distribution, wt % C5− 1.70 1.68 1.691.57 MeOH 1.16 0.35 1.15 2.43 BENZENE 0.24 0.20 0.24 0.22 TOLUENE 65.1767.30 73.76 83.83 EB 0.06 0.05 0.05 0.03 P-XYL 29.99 28.55 22.09 11.50M-XYL 1.16 0.72 0.34 0.13 O-XYL 0.52 0.35 0.21 0.11 ETOL 0.31 0.28 0.210.11 TMBENZENE 0.63 0.46 0.27 0.07 C10+ 0.06 0.05 0.00 0.00 100.00100.00 100.00 98.43 Performance Data Toluene Conv. % 29.73 27.44 20.479.62 MeOH Conv. % 97.81 95.17 84.14 66.42 MeOH Utilization, 59.02 59.0249.02 32.20 mol % p-Xylene Selectivity, % 94.70 96.38 97.58 97.95 XyleneYield on Tol, 34.14 31.93 24.40 12.66 wt % p-Xylene Yield on Tol, 32.330.8 23.8 12.4 wt % Xylenes/Aromatic 96.1 96.6 96.7 96.5 Product, wt %

Comparative Example A

ZSM-5 crystals were prepared according to the method set forth inExample 33 of the Butter et al U.S. Pat. No. 3,965,209. The ZSM-5 had asilica to alumina molar ratio of about 70 to 1 and was combined with analumina binder in a ratio of 65 weight % zeolite and 35 weight % binder.

The bound, phosphorus-free catalyst had an n-hexane sorption capacity,Q, of 74.4 mg/g and a Diffusion Parameter for 2,2-dimethylbutane of 740sec⁻¹. The catalyst was steamed at 950° C. for 65 hours at atmosphericpressure (100 kPa) in 100% steam which reduced its n-hexane sorptioncapacity, Q, to 32.4 mg/g, or 44% of the initial capacity, and itsDiffusion Parameter for 2,2-dimethylbutane to 1.72 sec⁻¹. The steamedcatalyst was then subjected to catalytic testing in the same manner asExamples 1-9. In particular, experiments were conducted at 600° C., 40psig (380 kPa), H₂/HC=2, H₂O/HC=2, WHSV=4 with a toluene/MeOH=2 feed.The results are summarized in Table 5, which provides data for anaverage analysis of three samples taken at 28.53. 33.32 and 37.22 hourson stream.

TABLE 5 Temp, ° C. 600 Pressure, psig 39.63 WHSV 4.00 Time on Stream, hr33.0 Product Distribution, wt % C5− 0.36 DME 0.09 MeOH 1.35 BENZENE 0.19TOLUENE 71.91 EB 0.05 P-XYL 21.40 M-XYL 1.91 O-XYL 1.18 ETOL 0.17TMBENZENE 1.29 C10+ 0.09 100.00 Performance Data Toluene Conv. % 22.30MeOH Conv. % 80.74 MeOH Utilization, mol % 53.79 p-Xylene Selectivity, %87.37 Xylene Yield on Toluene, wt % 26.47 p-Xylene Yield on Toluene, wt% 23.1 Xylenes/Aromatic Product, wt % 93.2

The data in Table 5 show that in Comparative Example A, although thetoluene conversion was 22.30%, the para-selectivity was only 87.37%, themethanol conversion was only 80.74% and the wt % xylenes based on thetotal aromatic product was only 93.2. Furthermore, the yield of theunwanted byproduct, trimethylbenzene, was 1.29 wt. %.

EXAMPLES 10-14

A series of fluid bed catalysts were produced containing about 4 wt %phosphorus and 25 wt. % of a 450:1 SiO₂/Al₂O₃ ZSM-5 in a bindercomprising kaolin clay. The catalysts were steamed for 0.75 hours atvarying temperatures between 1025 and 1060° C. and were used to effectthe alkylation of toluene with methanol in a bench-scale fluid bedreactor in the absence of cofed hydrogen. Details of the test and theresults obtained are summarized in Table 6 and FIG. 1. It will be seenthat, as the Diffusion Parameter of the catalyst decreased withincreasing steaming severity, the para-xylene selectivity increasedgenerally linearly whereas the para-xylene yield increased to a maximumat a D/r² value of 1-2×10⁻⁶ sec⁻¹ before decreasing again.

TABLE 6 Example No. 10 11 12 13 14 Catalyst Properties Phosphorus, wt %3.9 3.8 4.1 4.1 3.8 Steaming Temp, C. 1025 1031 1033 1033 1060 D/r²,sec-1 (×10⁶) 1.14 0.71 2.81 6.5 0.45 Q, (n-C6) mg/g 19.7 19 14.1 14.217.8 Parent Q, mg/g 21.6 21.6 17.1 20.7 21.9 Reaction Conditions FeedToluene/Methanol 2.08 2.03 1.93 2.06 2.17 (mol/mol) Feed H2O/HC(mol/mol) 0.47 0.46 0.63 0.63 0.51 Reactor Temp, F. 1105 1107 1113 11081110 Reactor P, psig 20.6 20.7 20.8 21.7 20.7 HC WHSV 1.71 1.75 1.751.72 1.71 Time On Stream, Hrs 10 10 10 10 2 Feed Composition, wt % MeOH12.81 13.12 13.20 12.50 12.26 Toluene 76.76 76.53 73.19 73.93 76.51 H2O10.43 10.35 13.61 13.57 11.23 Product Composition, wt % C5− 1.46 1.651.67 1.52 2.41 MeOH 0.01 0.03 0.09 0.01 0.29 Benzene 0.40 0.31 0.33 0.340.32 Toluene 54.60 55.89 50.81 52.41 62.16 EB 0.05 0.05 0.05 0.05 0.04p-Xylene 22.15 21.68 21.72 19.85 15.70 m-Xylene 1.87 1.16 2.33 2.94 0.42o-Xylene 0.78 0.50 1.00 1.25 0.20 Styrene 0.02 0.02 0.02 0.02 0.02E-Toluene 0.25 0.25 0.23 0.23 0.20 TMBenzene 0.52 0.48 0.70 0.72 0.24C10+ 0.28 0.34 0.31 0.30 0.39 H2O 17.61 17.64 20.74 20.36 17.61Performance Data Toluene Conv. % 28.9 27.0 30.6 29.1 18.8 MeOH Conv. %99.9 99.8 99.3 99.9 97.6 MeOH Utilization, 58.5 53.8 57.7 58.1 41.1 mol% p-Xylene Selectivity, % 89.3 92.9 86.7 82.6 96.2 Xylene Yield on Tol,32.3 30.5 34.2 32.5 21.3 wt % p-Xylene Yield on Tol, 28.9 28.3 29.7 26.820.5 wt % Xylenes/Aromatic 95.7 95.3 95.0 94.8 94.8 Products, wt %

EXAMPLE 15

A series of three catalysts similar to those of Examples 10-14 (25 wt %ZSM-5 of 450:1 silica/alumina ratio, 75 wt % clay binder with additional4 wt % phosphorus) was prepared by doping respectively with calcium(2000 ppmw added), magnesium (5000 ppmw added), and both calcium andmagnesium (2000 ppmw Ca/5000 ppmw Mg added). Slurries were prepared bymixing together components in the following order: ZSM-5 slurry,phosphoric acid, calcium/magnesium (from nitrate salts), and clay.Catalysts were spray dried and then air calcined at 540° C. for 3 hours.Three samples of each catalyst were then steamed for 45 minutes in 1atmosphere steam at 950° C., 1000° C., and 1050° C., respectively. Then-hexane sorption capacity and the Diffusion Parameter of the catalystsare plotted against steaming temperature in FIGS. 2 and 3. The presenceof magnesium (and calcium to a lesser extent) decreases the steamingtemperature required to produce a catalyst with a given DiffusionParameter. These data show that combinations of oxide modifiers caneffectively be used to produce the desired catalyst.

EXAMPLE 16

A comparison was made between a catalyst similar to those used inExamples 10-14, in which the initial zeolite had a silica/alumina molarratio of 450, and a catalyst produced from ZSM-5 having an initialsilica/alumina molar ratio of 26. In each case the catalyst containedabout 4 wt % phosphorus and 25 wt. % of ZSM-5 in a binder comprisingkaolin clay and was steamed for 45 minutes at >1000° C. before beingused to effect the alkylation of toluene with methanol in a fixed bedmicrounit. The results are summarized in Table 7 from which it will beseen that the 26:1 material had significantly lower activity (asindicated by the lower WHSV necessary to achieve comparable tolueneconversion), lower para-selectivity and lower methanol utilization thanthe 450:1 material.

TABLE 7 Catalyst Properties Percent ZSM-5 25 25 Si:Al Ratio 450 26Steaming Temperature, ° C. 1051 1016 Reaction Conditions Temperature, °C. 600 585 Pressure, psig 40 40 WHSV 8.0 2.50 Tol/MeOH (mol/mol) 2.02.00 H2/HC (mol/mol) 2.0 2.00 H2O/HC (mol/mol) 2.0 2.00 Time on Stream,hr 14.30 6.00 Product composition, wt % C5− 0.05 2.12 DME 0.00 0.00 MeOH0.40 0.32 BENZENE 0.13 0.23 TOLUENE 64.42 65.83 EB 0.06 0.05 P-XYLENE32.66 27.82 M-XYLENE 0.94 1.81 O-XYLENE 0.42 0.75 ETHYL TOLUENE 0.330.25 TMBENZENE 0.56 0.76 C10+ 0.04 0.06 Performance Data Toluene Conv.,% 30.68 29.16 MeOH Conv., % 94.30 95.43 MeOH Utilization, mol % 67.3759.46 p-Xylene Selectivity, % 96.02 91.58 Xylene Yield on Tol, wt %36.61 32.69 p-Xylene Yield on Tol, wt % 35.2 29.9 Xylenes/AromaticProducts, wt % 96.8 95.7

EXAMPLES 17 and 18

Two composite catalysts were produced containing 10 wt % of 450:1SiO₂/Al₂O₃ ZSM-5 in a kaolin clay matrix which in one case alsocontained 2.8 wt % phosphorus (Example 17) and the other case did notcontain phosphorus (Example 18). Each catalyst was steamed at 1010° C.for 0.75 hour and was then used to effect the alkylation of toluene withmethanol in a bench-scale fluid bed reactor containing 80 grams ofcatalyst. The properties of the steamed catalysts and the results of thetoluene alkylation tests are shown in Table 8 below.

From Table 8 it will be seen that the Diffusion Parameter, D/r² of thephosphorus-free catalyst of Example 18 remained high after steaming. Inaddition, it will be seen that the para-xylene selectivity and yield ofthe phosphorus containing catalyst of Example 17 were significantlyhigher than those of the phosphorus-free catalyst of Example 18.

TABLE 8 Example 17 18 Catalyst Properties Phosphorus, wt % 2.8 0 D/r²,sec⁻¹ (×10⁶) 2.54 36.28 Q, (n-C6) mg/g 8.1 8.8 Parent Q, mg/g 8.4 10.6Feed Composition, wt % MeOH 12.82 13.15 Toluene 75.61 75.61 H2O 11.5711.24 TOTAL 100 100 Reaction Conditions Feed Toluene/Methanol (mol/mol)2.05 2.00 Feed H2O/HC (mol/mol) 0.53 0.51 Reactor Temp, F. 1107 1108Reactor Pressure, psig 19 21.6 HC WHSV 1.72 1.74 Time On Stream, Hrs 6 6Product Composition, wt % C5− 1.66 1.53 MeOH 0.34 0.33 Benzene 0.26 0.31Toluene 55.09 54.33 EB 0.04 0.03 p-Xylene 20.08 15.94 m-Xylene 1.57 4.83o-Xylene 0.72 2.3 Styrene 0.02 0.01 E-Toluene 0.23 0.17 TMBenzene 0.611.49 C10+ 0.29 0.25 H2O 19.09 18.48 TOTAL 100 100 Performance DataToluene Conv. % 27.1 28.1 MeOH Conv. % 97.3 97.5 MeOH Utilization, mol %54.1 54.3 p-Xylene Selectivity, % 89.8 69.1 Xylene Yield on Tol, wt %29.6 30.5 p-Xylene Yield on Tol, wt % 26.6 21.1 Xylenes/AromaticProducts, wt % 94.9 92.2

EXAMPLES 19-21

A base catalyst particle was prepared by spray-drying a mixture of ZSM-5having a silica-alumina molar ratio of 450: 1, kaolin clay and silica.After rotary calcination at 650° C. (1200° F.), the final composition ofthe catalyst was 40 wt % ZSM-5, 30 wt % kaolin and 30 wt % silica. Thecalcined catalyst was divided into three samples, which were impregnatedby the incipient wetness techniques with solutions containing boron(Example 19), magnesium (Example 20) and lanthanum (Example 21)respectively and having the following compositions:

a) boron-containing solution

20 gm boric acid

800 gm distilled water

8 gm 30 wt % ammonium hydroxide

b) magnesium-containing solution

20 gm magnesium nitrate hexahydrate

240 gm distilled water

c) lanthanum-containing solution

20 gm lanthanum nitrate hexahydrate

80 gm distilled water.

In each case, impregnation was conducted by incipient wetness by adding0.79 gm of the appropriate solution to a catalyst sample, after whichthe sample was dried at 150°C. for 2 hours and then air calcined at 550°C. for 4 hours to convert the ammonium and nitrate salts to oxides. Theoxide-modified catalysts were then heated in 1 atmosphere steam at 1000°C. Table 9 lists the oxide loading on each catalyst on an elementalbasis and the n-hexane adsorption capacity (Q in mg/g) and DiffusionParameter (D/r²×10⁶ sec⁻¹) of the unsteamed and steamed catalysts.

TABLE 9 Oxide Loading Q (n-C₆, mg/g) D/r² sec⁻¹ (×10⁶) Un- steamedCatalyst Example 0.2 wt % boron 52.6 17 19 Example 0.5 wt % magnesium42.7 24.2 20 Example 4.9 wt % lanthanum 39.8 19.9 21 Steamed CatalystExample 0.2 wt % boron 32.7 2.6 19 Example 0.5 wt % magnesium 37.3 9.420 Example 4.9 wt % lanthanum 31.1 1.4 21

The steamed catalysts of Examples 19 and 21 were then tested in thealkylation of toluene with methanol under the conditions and with theresults listed in Table 10.

TABLE 10 Example 19 21 Reaction Conditions Temperature, C. 592 592Pressure, psia 16 16 WHSV 3 4 Time on stream, minutes 402 6 ProductComposition, wt % C5− 2.33 2.47 Methanol 0.59 3.18 Benzene 0.07 0.04Toluene 64.6 67.54 Ethylbenzene 0.06 0.06 P-xylene 28.05 23.02 M-xylene1.81 1.47 O-xylene 0.75 0.61 Ethyltoluene 0.31 0.30 Trimethylbenzene1.08 0.78 C10+ 0.34 0.52 Performance Data % of total xylenes Para 91.691.71 Meta 5.90 5.85 Ortho 2.46 2.44 Total xylenes, wt % 30.61 25.10Xylenes/total aromatic product 94.46 93.81 Toluene conversion 30.2 25.9Methanol conversion 96.3 79.9 Methanol utilization 60 60

What is claimed is:
 1. A method for producing a catalyst for use in the selective production of para-xylene by reacting toluene with methanol, said method comprising the steps of: (a) starting with a porous crystalline material having a Diffusion Parameter for 2,2-dimethylbutane in excess of 15 sec⁻¹ when measured at a temperature of 120° C. and a 2,2-dimethylbutane pressure of 60 torr (8 kPa); and (b) contacting the material of step (a) with steam at a temperature in excess of 1000° C. to reduce the Diffusion Parameter thereof for 2,2-dimethylbutane to about 0.1-15 sec⁻¹ when measured at a temperature of 120° C. and a 2,2-dimethylbutane pressure of 60 torr (8 kPa), the micropore volume of the steamed material being at least 50% of the unsteamed material.
 2. The method of claim 1, wherein the porous crystalline material is combined with a source of at least one oxide modifier selected from the group consisting of oxides of elements of Groups IIA, IIIA, IIIB, IVA, VA, VB and VIA of the Periodic Table prior to step (b).
 3. The method of claim 1, wherein the porous crystalline material is combined with a source of at least one oxide modifier selected from the group consisting of oxides of boron, magnesium, calcium, lanthanum and phosphorus prior to step (b).
 4. The method of claim 1, wherein the porous crystalline material used in step (a) is an aluminosilicate zeolite having a Constraint Index of about 1 to
 12. 5. The method of claim 4, wherein the zeolite has a silica to alumina molar ratio of at least
 250. 6. The method of claim 1, wherein step (b) is conducted for about 10 minutes to about 100 hours.
 7. The method of claim 2, wherein the catalyst contains about 0.05 to about 20 wt % of the oxide modifier based on the elemental modifier.
 8. The method of claim 2, wherein the catalyst contains about 0.1 to about 10 wt % of the oxide modifier based on the elemental modifier.
 9. The method of claim 5, wherein said zeolite is ZSM-5 or ZSM-11.
 10. A process for the selective production of para-xylene which comprises reacting toluene with methanol under alkylation conditions in the presence of a catalyst produced by the method of claim
 1. 